Referring to FIG. 1, a conventional LED drive circuit uses a retract circuit 72 and a PWM (Pulse Width Modulator) 71 to provide a DC power source having constant current and power. A shortcoming is that the components of pulse width modulator and electromagnetic interference filter are costly.
Further, the conventional LED drive circuit does not incorporate a protection circuit of high voltage feedback compensation and if it uses a linear power source, although there is not electromagnetic interference, yet with the voltage of the increase AC power getting higher and higher, the voltage across a transistor of the circuit is getting higher and higher, making the input voltage of the AC power source excessively high and thus leading to fast increase of power (W) (see FIG. 2). Thus, it is not possible to protection the LED, leading to overheat and thus damage of the LED.
Thus, the present invention aims to provide an LED drive circuit that allows a transistor to operate in a linear zone without applying a switching frequency so as not to incorporate an electromagnetic interference filter and that comprises a protection of high voltage feedback compensation to prevent an increase of power caused by excessively high input voltage from an AC power supply.